An internal combustion engine may include one or more turbochargers for compressing a fluid, which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor driven by the turbine. The compressor receives the fluid to be compressed and supplies the compressed fluid to the combustion chambers. The fluid compressed by the compressor may be in the form of combustion air or an air/fuel mixture.
An internal combustion engine may also include a supercharger arranged in series with a turbocharger compressor of an engine. U.S. Pat. No. 6,273,076 (Beck et al., issued Aug. 14, 2001) discloses a supercharger having a turbine that drives a compressor to increase the pressure of air flowing to a turbocharger compressor of an engine. In some situations, the air charge temperature may be reduced below ambient air temperature by an early closing of the intake valve.
Early or late closing of the intake valve, referred to as the “Miller Cycle,” may reduce the effective compression ratio of the cylinder, which in turn reduces compression temperature, while maintaining a high expansion ratio.
Consequently, a Miller cycle engine may have improved thermal efficiency and reduced exhaust emissions of, for example, oxides of Nitrogen (NOx). Reduced NOx emissions are desirable. In a conventional Miller cycle engine, the timing of the intake valve close is typically shifted slightly forward or backward from that of the typical Otto cycle engine. For example, in the Miller cycle engine, the intake valve may remain open until the beginning of the compression stroke.
While a turbocharger may utilize some energy from the engine exhaust, the series supercharger/turbocharger arrangement does not utilize energy from the turbocharger exhaust. Furthermore, the supercharger requires an additional energy source.
The present invention is directed to overcoming one or more of the problems as set forth above.